Prostaglandins (PGs) are a class of naturally occurring compounds with a wide variety of physiological activities, which have a common prostanoic acid skeleton. Naturally occurring PGs are classified into PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs, PGIs and PGJs according to the structural characteristics of the 5-membered ring in the skeleton. It is and also classified into subclasses 1, 2, 3 and so on according to the ansaturation and oxidation. Various synthetic analogues of these PGs are known. Among these, PGI2, which is a typical PGI derivative, is called prostacycline (see Nature, vol. 268, p. 688, 1976). PGI2 is known as a substance having potent platelet aggregation inhibiting activity and peripheral vasodilator activity. Japanese Examined Patent Application Publication Nos. 2-12226, 2-57548 and 1-53672 have described 4,8-inter-m-phenylene PGI2 derivatives, in which the exo-enol ether moiety that is a structurally characteristic portion of PGI2 is converted to an inter-m-phenylene moiety to substantially improve the instability of PGI2. However, it has not yet recognized that such derivatives have therapeutic activities on renal failure.
Renal failure is a condition characterized by decreased number of functional nephrons, resulting in reduced excretion of nitrogenous metabolic products and eventually causing the failure to maintain homeostasis in the biological environment. Specifically, this can be said to be a condition in which blood urea nitrogen (BUN) and creatinine levels are continuously increased. Renal failure is categorized into two primary types: acute renal failure in which the onset is abrupt and recovery may occur; and chronic renal failure which is slowly progressive but irreversible.
Acute renal failure is primarily categorized into the following two types: oliguric acute renal failure which is frequently complicated by water, electrolyte and acid-base imbalances and manifested by oliguria or anuria; and non-oliguric acute renal failure in which decreased urinary volume is not found.
Acute renal failure is also categorized into the following three types according to its cause: 1) pronephric acute renal failure in which reduction of renal blood flow occurs due to systemic hemodynamic changes such as prerenal dehydration and shock, causing reduced glomerular filtration rate; 2) renal acute renal failure which is induced by glomerular and tubular disorders such as acute tubular necrosis; and 3) postrenal acute renal failure which is caused by obstruction of the urinary tract, e.g., by a calculus. According to the clinical manifestations, it can also be categorized into oliguric, uretic and recovery stages. In the treatment of acute renal failure, it is important to track down its cause and sufficiently perform systemic control of the patient. Such treatment includes two major forms, conservative treatment and dialytic treatment. According to the conservative treatment, in the oliguric stage, excessive water drinking is avoided and the amount of protein intake is restricted, while simultaneously supplying a sufficient amount of calories. In the oliguric stage, or when heart failure has occurred, then sodium intake is restricted. In contrast, in the uretic stage, potassium intake is increased. Generally in the oliguric stage, calcium intake is restricted. In the case where BUN is 60 mg/dl or higher or rises by 30 mg/dl or more per day or hyperkalemia or heart failure is found, then it is recommended to perform an early frequent dialysis.
Chronic renal failure is a condition in which gradual reduction in renal functions occurs due to a chronically progressive renal disease, in which the reduced renal functions are manifested as the insufficiency of all functions for which the normal kidney is responsible. The causal diseases of chronic renal failure are all of the nephropathic diseases, including primary renal diseases, nephropathy in systemic diseases, congenital renal diseases, renal infections, nephropathy induced by any nephrotoxic substance and obstructive urinary diseases. As seen in the clinical background of patients to whom dialysis has been introduced for treatment of chronic renal failure, the primary causal diseases of chronic renal failure may include chronic glomerulonephritis, diabetic nephropathy, chronic pyelonephritis, nephrosclerosis and cystic kidney. Among these, chronic glomerulonephritis and diabetic nephropathy make up a large proportion. The proportion of diabetic nephropathy as the causal disease in the total cases, however, remarkably increases as the number of diabetic patients rapidly increases in recent years.
As stated above, renal failure may be caused by various diseases. However, all types of renal failure have particular common clinical manifestations regardless of their causal diseases, such as lung congestion and congestive heart failure associated with reduced urinary volume; neurological or mental complaints associated with advanced uremia; anemia caused by reduced production of erythropoietin in the kidney; electrolyte imbalance, such as hyponatremia and hyperkalemia; gastrointestinal complaints; defect of bone metabolism; and defect of carbohydrate metabolism.
For the treatment of chronic renal failure in the conservative stage, dietary therapy including a low-protein, high-calorie diet is basically employed. In this case, it is required to restrict sodium chloride intake and water intake and to use an antihypertensive agent to control the hypertention which may be a risk factor for exacerbation of renal failure. However, such dietary therapy and the treatment with an antihypertensive agent as mentioned above produce unsatisfactory effects. Therefore, the number of patients who inevitably have hemodialysis goes on increasing year by year due to the manifestation of uremic symptoms caused by the advanced disorders of renal functions. In patients with renal failure who have entered into dialysis, remarkable improvement in the rate of prolongation of life has been achieved due to the improved hemodialysis therapy in recent years. However, there still remain problems in that the patients are unavoidable to visit the hospital twice or three times a week, that defects of erythrocyte production or maturation may occur, that complications will follow which may caused by the accumulation of aluminum and β2-microglobulin in a body occurring after the long-term dialysis, and so on.
The object of the present invention is to provide a therapeutic agent for renal failure on which already-existing drugs or agents show unsatisfactory effects.